I. DIAGNOSTICS FOR ORBITAL DISEASES
Orbital diseases are traditionally divided into: exophthalmia and enophthalmia. Useful diagnostics beyond the ophthalmic examination are ultrasonography and radiology. Newer imaging techniques, including CAT scan and MRI, provide additional insight for space-occupying masses.
II. CONGENITAL/DEVELOPMENTAL: Anophthalmos/Microphthalmia
Complete absence of the eye (anophthalmos) is very rare. In microphthalmia, an abnormally small globe is associated with other ocular defects. A small but otherwise normal globe is called nanophthalmia. In microphthalmia, vision may be normal, reduced, or absent. In the Doberman Pinscher, microphthalmia is associated with anterior segment dysplasia and retinal dysplasia. Congenital cataracts and microphthalmia are inherited in the Miniature Schnauzer. Microphthalmia with multiple ocular anomalies (equatorial staphylomas, persistent pupillary membranes, cataracts, retinal dysplasia, and retinal detachments) occur in homozygous merles of many breeds.
A. Inflammatory Lesions: Orbital Cellulitis/Abscess
Orbital inflammatory diseases are rather common in the dog. One series involved 13 dogs with a mean age of 4 years. Typically, dogs present with acute and usually unilateral exophthalmos, protrusion of the nictitating membrane, and conjunctival hyperemia. There may be serous to mucopurulent ocular discharge, and palpation of the globe and periorbital area as well as opening the mouth are extremely painful. There may be a fluctuating swelling of the oral mucosa behind the last ipsilateral molar tooth. Affected dogs are usually febrile and anoretic. White-blood-cell counts may reveal neutrophilia.
Causes include foreign material, porcupine quills, and spread of hematogenous infections, oral cavity, sinuses, and tooth root infections. Pasteurella sp.have been cultured from five of 14 orbital abscesses. The treatment of orbital cellulitis is drainage by incision of the oral mucosa behind the last upper molar tooth; systemic antibiotics; hot packs; and topical antibiotics. If the exophthalmos increases temporarily after drainage, a temporary tarsorrhaphy may be necessary. The prognosis is usually good. In treated most cases, the exophthalmos regresses within 36 to 48 hours, and the general condition of the animal improves markedly. If foreign material is retained in the orbit, recurrences or abscess formation is possible.
B. Salivary Retention Cysts and Mucoceles
Leakage of saliva from the zygomatic gland or its excretory duct causes orbital inflammation and tissue fibrosis. This fluctuating swelling can be dorsolateral or ventromedial orbit; dorsal or ventral in the conjunctiva, or in the oral cavity. Exophthalmos and protrusion of the nictitating membrane are usually present. Mucoceles are best treated by surgical excision of the cyst and associated gland.
Because of the absence of a bony orbital wall laterally, swelling or atrophy of the masticatory muscles can displace the globe forward. Also inflammatory diseases of the extraocular muscles may produce exophthalmos and strabismus.
1. Extraocular polymyositis of the extraocular muscles has been recently described causing exophthalmos and impaired mobility of the globes. Extraocular polymyositis has been diagnosed in Golden Retrievers, Hovawart, and Mountain dog crosses.
2. Masticatory/eosinophilic myositis predominantly affects young German Shepherds, Weimaraners, Labrador Retrievers, and Golden Retrievers, and occurs as an acute disease accompanied by fever and anorexia. Jaw movements are limited and painful because masseter muscle is swollen and painful. Bilateral exophthalmos, protrusion of the nictitating membrane, and congestion of episcleral vessels are often presenting signs; in chronic cases, exposure keratitis may ensue. Without treatment, inflammatory episodes run for one to three weeks. With repeated acute attacks, fibrosis of the masticatory muscles eventually result in muscle atrophy and enophthalmos.
Leukocytosis with variable eosinophilia and increased levels of creatine phosphokinase may be present. Biopsy of affected muscle is usually diagnostic with degeneration of muscle fibers, and infiltration by neutrophils and eosinophils. Therapy consists of immunosuppressive doses of oral corticosteroids over 3 to 4 weeks. Azathioprine treatment is another possibility. Recurrence is likely with progressive muscle loss and fibrosis.
D. Orbital Neoplasms
Obital Neoplasms generally occur in older animals (mean age 9.5 years). Orbital tumors usually cause slowly progressive, unilateral exophthalmos, with variable displacement of the globe. Bilateral orbital neoplasms appear rare except for lymphosarcoma.
Orbital neoplasms are not initially painful, and retropulsion of the globe is decreased or impossible. In most cases vision is retained, however tumors arising from the optic nerve or its meninges may cause blindness at an early stage. Orbital tumors are mostly primary (60-70%) and malignant (80-90%). Fibroma, meningioma, osteosarcoma, and lymphosarcoma were the most common neoplasms diagnosed in one series; in another, osteosarcoma and mastocytoma predominated. After localization of the lesion, a fine-needle aspirate is obtained for a definite diagnosis. Complete physical examination, and chest radiographs are indicated.
Most orbital masses that can be localized without evidence of distant metastasis may be surgically removed while preserving the globe and, possibly, the animal's vision, but usually have a poor prognosis. Exenteration of the globe or radical orbitectomy may be also considered.
E. Traumatic Diseases
1. Orbital hematoma and often subconjunctival hemorrhages may result from road accidents. These multi traumatized patients present with marked exophthalmos, lagophthalmos, and secondary xerophthalmia. Injury of the globe is often involved. Massive orbital hemorrhage is often associated with partial to complete proptosis of the globe. Ultrasonography of the globe is indicated when hyphema prevents examination of the inner eye.
In cases of extensive scleral rupture, enucleation is the best treatment option. Phthisis bulbi is a common sequela of globe contusions. To prevent serious exposure keratitis, a third eyelid flap or a temporary tarsorrhaphy is indicated.
2. Orbital emphysema is usually a complication of enucleation, and from fractures of the frontal sinus. Brachycephalic dogs appear predisposed.
3. Proptosis results from a sudden, forward displacement of the globe with simultaneous entrapment by the eyelids behind the equator. In one series 50% of the dogs were brachycephalic breeds. In dolichocephalic breeds, greater trauma is necessary to cause proptosis. Proptosis of the globe is a true ophthalmic emergency.
Prognosis depends on: time, breed of dog, other injuries, pupil size, and condition of the cornea. About 40% of proptosed globes regain some functional vision (dogs); in cats very few eyes regain vision. Proptosed eyes should be repositioned under general anesthesia as soon as possible. Lateral canthotomy is used to enlarge the palpebral fissure and a temporary complete tarsorrhaphy is necessary to protect the eye and maintain the globe within the orbit.
The eyelid sutures are removed once a brisk blink reflex returns and orbital swelling has resolved. Sequelae of proptosis include blindness, strabismus, lagophthalmos, sensory deficit of the cornea, keratoconjunctivitis sicca, exposure keratitis, glaucoma, and phthisis bulbi.
4. Orbital fractures involving the frontal, temporal, and zygomatic bones are not uncommon after head trauma. Clinical signs include exophthalmos or enophthalmos, strabismus, retrobulbar and periocular hemorrhage, pain, lacrimation, and facial asymmetry. Small, nondisplaced fractures stabilize spontaneously and do not require surgical reduction and fixation; large and unstable fractures may require internal fixation.
5. Orbital foreign bodies/shotgun injuries. Orbital foreign bodies and gunshot injuries often present as acute inflammatory diseases. Foreign bodies may enter the orbit from the oral cavity or through the conjunctival sac. Organic foreign bodies are not recognized on plain radiographs, but gunshot pellets are easily demonstrated.
In enophthalmia, the globe is less prominent because of the loss of globe size, and/or reduction in orbital tissues. Reduced globe size is associated with microphthalmia or phthisis bulbus (atrophy of the eye; usually secondary to intraocular inflammation; or glaucoma). Enophthalmia may also occur with loss of orbital fat; dehydration; orbital fibrosis; following orbital surgery; Horner's syndrome; in the medial 'pocket syndrome' of large and giant dogs; and from other diseases.
V.SURGERY OF GLOBE AND ORBIT
Enucleation is the most common orbital surgery and consists of the removal of the globe. Enucleation is recommended for cases of blind, painful eyes (e.g., uncontrollable glaucoma, endophthalmitis, intraocular neoplasms, and severe ocular trauma with hemorrhage). The most commonly used surgical technique is the subconjunctival approach which removes the globe, nictitating membrane, and lid margins.
Exenteration involves removal of the conjunctiva, periorbita, extraocular muscles, and globe, and with orbital tumors is extended to involve all orbital contents. A transpalpebral enucleation approach is used, and all of the orbital tissues excised.
C. Orbital prosthesis
To improve the cosmetic appearance after enucleation or exenteration, silicone or methyl methacrylate spheres may be implanted. Silicone spheres are most commonly used. Possible complications include wound dehiscence, extrusion of the implant, traumatic dislocation and rotation of the implant, orbital seroma, and infection.
D. Evisceration and implantation of the intrascleral prosthesis
Blind and painful eyes without septic endophthalmitis or intraocular neoplasms may be treated by evisceration and implantation of a silicone prosthesis. Blind eyes with aseptic uveitis and beginning phthisis bulbi can equally be fitted with an intrascleral prosthesis to prevent further shrinkage of the globe and secondary adnexal problems.